The crossing is the key device in an overhead contact system that provides the electrical and mechanical transition between different tracks, and its condition directly affects smooth pantograph passage and pantograph-catenary safety. To ensure that crossing equipment performs reliably and meets its parameter requirements, this technical quality standard and workmanship has been drawn up, and applies to the routine measurement, inspection and maintenance of crossings in the overhead contact systems of conventional-speed railways.
1. Purpose and Main Content of the Work
The core purpose of crossing maintenance is to establish accurately, through periodic measurement and targeted inspection, the technical parameters, dynamic running characteristics and safety condition of the crossing, so that hidden defects are found and eliminated in good time and the OCS equipment is kept in good operating condition.
The main content of the work falls into the following three levels:
Measurement items: measure in particular the longitudinal and transverse position of the turnout registration post, the stagger at the registration points on both sides of the crossing point, the exact projected position of the crossing point, the height difference between the two contact wires at 500 mm and at 800 mm apart, and the extent of the first-contact zone.
Inspection items: check on site whether the limiting tube is correctly installed and positioned and whether its freedom of movement is normal; confirm that there are no clamps or other parts in the first-contact zone that could strike the pantograph; observe the attitude of the pantograph as it passes; and check the tightening torque of all connecting bolts.
Maintenance items: make precise adjustments and repairs to any part found out of standard or in poor condition during measurement and inspection, including correction of the stagger at registration points, adjustment of the height difference between contact wires, adjustment of the limiting tube clearance, replacement of components and anti-corrosion treatment.
2. Scope, Intervals and Working Conditions
This standard applies to the measurement, inspection and maintenance of all crossings in the conventional-speed overhead contact systems within the area of responsibility. The working intervals and conditions are as follows:
Measurement interval: once every 6 months, carried out within a railway possession.
Maintenance interval: carried out together with the comprehensive inspection programme, generally within a possession and using an OCS maintenance vehicle or a ladder trolley as the working platform.
3. Preparation for the Work
Before work begins, personnel, tools and equipment, materials and technical documentation must all be fully prepared.
Personnel: members of the work team must have received specialist training, be able to adjust crossings and be familiar with the safety rules.
Tools and equipment: laser measuring instrument or track gauge, torque wrench, spirit level, single pulley, ropes, wire slings, fine wire brush, hexagon socket keys, and a full set of safety protection, lighting, communications and image recording equipment.
Materials: carry limiting tubes, droppers and clamps, registration clamps, bonding conductors and clamps, Φ4.0 mm galvanised iron wire, electrical contact grease, temperature-indicating strips and binding wire as required by the maintenance work.
Technical documentation: carry the OCS layout plan for the section concerned, the crossing design and installation drawings, and the record of the previous maintenance.
4. Working Procedure and Adjustment Methods
(1) Inspection content
The work team must check the following points item by item: whether the projected position of the crossing point lies within the standard range of the track gauge between the two inner rails on the turnout lead curve; whether the stagger at the registration points and the contact wire height are compliant; whether the position of the limiting tube and the internal freedom of movement meet the requirements; whether there are foreign objects or clamps in the first-contact zone; whether the height difference between the two contact wires at 500 mm and at 800 mm apart is out of tolerance; whether the bonding conductor clamps and temperature-indicating strips are intact; and whether any connecting bolt has loosened.
(2) Specific adjustment methods
1. Adjustment of a crossing on a single turnout
Transverse offset only: if the longitudinal position of the crossing point is correct but it deviates transversely from the bisector of the angle between the two inner rails, loosen the registration supports on both sides and shift both contact wires together to the standard position.
Longitudinal offset only: if the crossing point lies longitudinally beyond the 1050 mm range, increase the crossing angle between the two wires; if it lies within less than the 735 mm range, reduce the crossing angle. The angle is adjusted by changing the stagger at the registration points, but the stagger should in principle be kept within 300~400 mm and must not exceed 450 mm.
Both transverse and longitudinal offset: first remove the limiting tube and adjust the working contact wire to the standard registration stagger; then use measuring tools to locate on the working wire the theoretical crossing point that satisfies the projected position requirement; then adjust the stagger of the non-working wire so that the two crossing points coincide; and finally refit the limiting tube in the new position.
Adjusting the contact wire height difference: having ensured that the height of the lower contact wire meets requirements, adjust the height of the other wire by slackening or tightening the adjacent droppers. Use a spirit level to measure precisely the height difference at 500 mm and at 800 mm apart, ensuring that at a main line crossing the branch line is 15~25 mm higher than the main line, and that at a branch line crossing the height difference between the two wires is not more than 20 mm.
Adjusting the freedom of movement in the limiting tube: check the relative movement allowance of the two contact wires within the limiting tube and adjust the clearance by adding or removing shims so that the wires can expand and contract freely with temperature while jamming is prevented.
Bonding conductors and other components: check and tighten the bonding conductor clamps in accordance with the bonding maintenance workmanship, tighten all connecting bolts alternately and evenly, and remove rust and apply oil to corroded parts or replace them.
2. Adjustment of a crossing on a double slip turnout
On a double slip turnout there are crossing point offsets in both the long axis and the short axis directions. If the short axis direction is correct but the long axis direction is offset, move the two registration devices towards or away from each other to correct the long axis crossing point; if the long axis direction is correct but the short axis direction is offset, shift both registration devices in the same direction; if both axes are offset, first adjust one contact wire to the midpoint of the centre axis offset and then bring the other contact wire to meet it at that point.
3. Adjustment of a crossing on a scissors crossover turnout
A scissors crossover contains several single turnouts together with one diamond crossing. First adjust the contact wire positions at turnouts A, B, C and D separately to the single turnout standard so that the stagger and the projected crossing position are compliant; then check whether the crossover crossing point O lies directly above the centre of the diamond crossing, correcting any deviation by adjusting the stagger on both sides; and finally recheck the limiting tube clearances and the contact wire height differences at all crossings.
5. Control Measures for the Main Safety Risks
Preventing trapping and derailment of the trolley: when working from a ladder trolley, watch the direction in which the turnout is set and never place feet or tools between the switch rail and the stock rail; keep constant watch on the path of the trolley to prevent it from leaving the rails.
Preventing track circuit short circuits: during measurement and adjustment, take great care that metal tools do not touch both rails at once or bridge both sides of an insulated joint, which would produce a false occupied indication in the signalling system.
Preventing injury from sudden release of conductors: before adjusting a non-working wire or removing components, take measures against slipping, and staff must not stand on the side towards which the conductor is under load.
Ensuring smooth pantograph transition: the raising of the non-working wire should change evenly towards the anchoring direction, so that there is no hard point or abrupt change of gradient within the first-contact zone.
Correct bolt tightening: tightening torque must be applied alternately and evenly, and components must never be struck with a hammer, to avoid seizing of the threads or damage to the parts.
Protection against wear at the crossing: if the non-working wire bears heavily upwards against the limiting tube, or if the clearance at the point where the messenger wires cross is less than 60 mm, check whether they are rubbing against each other and, where necessary, fit protective strips or adjust the conductor heights.
Recheck after the work: on completion, the dynamic pantograph envelope must be rechecked to confirm that no component intrudes into it, so that traffic safety is assured.
6. Summary of the Principal Technical Standards
At a crossing between a main line and a branch line, the main line contact wire should lie below the branch line wire; where both lines are branch lines, the one nearer the centre anchorage lies below.
On a single turnout the standard position of the crossing point is the transverse midpoint of the 735~1050 mm range of track gauge between the two inner rails on the turnout lead curve, with a permitted deviation of ±50 mm; longitudinally it lies more than 2.5 m from the turnout registration point.
Where the two working contact wires are 500 mm and 800 mm apart, at a main line crossing the branch line should be 15~25 mm higher than the main line, and at a branch line crossing the height difference should not exceed 20 mm; the non-working wire should be raised by 60~90 mm at 800 mm from the track centre and blended evenly.
The length of the limiting tube should comply with the design, and an appropriate freedom of movement should be left inside it.
No clamp of any kind may be installed within the first-contact zone, that is between 600~1050 mm from the centre of the other track.
The vertical spacing where two messenger wires cross should not be less than 60 mm.
For the crossing point position deviation on double slip and scissors crossover turnouts, the warning value is ±100 mm and the limit value is ±150 mm.
Strict application of the technical quality standards and workmanship set out above effectively safeguards the long-term stable operation of OCS crossings and provides solid support for railway traffic safety.
